The invention relates to a safety system for a motor vehicle, including a sensor, coupled to an evaluation unit, for predicting an impending collision, a control device for triggering a first device to cause a rearward displacement of at least one vehicle occupant at a predetermined first time instance prior to the predicted collision.
Safety systems in motor vehicles are primarily provided to protect vehicle occupants from injuries or reduce such injuries in the event of an impact. Examples of such safety systems are airbags, shiftable steering systems, or belt tensioners. Originally, activation of such safety systems took place in terms of time only after an impact. In the meantime, safety systems have been proposed which enable activation already before a collision.
DE 10 2011 108 915 A1 describes a restraining device for a motor vehicle, using a sensor to determine an impending impact. When recognizing an impending collision, the vehicle occupants are shifted backwards to thereby attempt a reduction of a speed differential between the vehicle occupants and the vehicle at the time of the impact. In this way, stress on the vehicle occupants shall be minimized. The rearward displacement can be realized by a controlled movement of the vehicle seat. In this safety system, the phase to couple the vehicle occupants to the deceleration of the vehicle occurs only after the impact has begun. At the beginning of the collision, there exists a certain elasticity. However, efforts are underway to realize a best possible coupling of the vehicle occupants to the vehicle so as to minimize forces and accelerations acting on the vehicle occupants. The degree of coupling between a vehicle occupant and the vehicle is indicated by the ride-down effect or respective RDE value which may range between 0% and 100%. A high RDE value is beneficial and means that a vehicle occupant is decelerated already when the collision begins.